overheating

Hi Kinda New here, I have a 2008 GMC W4500 Forward Crew Cab 6.0 lts, gas (basically is an NPR HD), with overheating problems, Water Pump, Thermostart, Fan clutch and even the head job has been done since it was overheated, but as I got the truck back, it runs fine cruising at 60 MPH, but if you...

This thing has been acting this way for the last week. If you switch on the PTO, switch off the Exhaust Brake, hit the switch to idle it up, and let it sit there running 30-45 minutes, with no change in temperature, but the minute you hook onto something and start winching, the temp gauge...